JP2001261324A - Method of recovering chlorosilanes - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of recovering chlorosilanes in high recovery from crude chlorosilanes which are obtained by chlorinating or hydrochlorinating metallurgical grade silicon and contain impurities such as aluminum chloride. SOLUTION: This method of recovering the chlorosilanes, comprising evaporating the chlorosilanes from the crude chlorosilanes containing aluminum chloride is characterized by evaporating the chlorosilanes by a thin film evaporation method and taking out the concentrated product of the aluminum chloride in a liquid state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a chlorosilanes solution containing impurities such as aluminum chloride obtained by chlorinating or hydrogen-chlorinating metallurgical grade silicon at a high recovery rate and for a long period of time. And a method of recovering while preventing scaling.

[0002]

2. Description of the Related Art Chlorosilanes obtained by chlorinating or hydrochlorinating metallurgical grade silicon include aluminum, iron, titanium and the like which are usually contained in metallurgical grade silicon in an amount of about 0.01 to 10% by weight. When the components are simultaneously chlorinated or hydrochlorinated, these chlorides, such as aluminum chloride, iron chloride, and titanium chloride, are contained as impurities.

[0003] These metal chlorides become undesirable impurities in the production process of semiconductor-grade high-purity silicon and photovoltaic-grade silicon, and thus need to be separated and removed from chlorosilanes.

Generally, these metal chlorides include trichlorosilane (hereinafter, referred to as TCS) and silicon tetrachloride (hereinafter, referred to as TCS).
Since it has a higher boiling point than useful chlorosilanes (hereinafter referred to as STC), there has been conventionally proposed a method in which chlorosilanes are evaporated and recovered using a distillation column to be separated as a residue.

However, the method for recovering chlorosilanes using the above distillation column has problems to be solved in industrial practice.

That is, among the above-mentioned metal chlorides, when aluminum chloride is concentrated to a certain degree or more in a chlorosilanes solution containing the same, scaling on the evaporation heating surface occurs, which not only lowers the evaporation efficiency but also reduces the evaporation efficiency. In some cases, the heating surface of the distillation column and the piping may be blocked.

When the above-mentioned blockage occurs, not only does the production process stop due to the open cleaning and the productivity is reduced, but also the blockage reacts violently with moisture, making the cleaning operation extremely dangerous. And had

It has been empirically known that the concentration of aluminum chloride at which scaling on the heating surface in the distillation column starts to occur is about 2% by weight in a normal temperature range (50 to 180 ° C.) in which chlorosilanes are evaporated. ing.

[0009] Therefore, conventionally, the lower part of the distillation column was appropriately extracted and discarded so that the aluminum chloride concentration did not exceed this concentration.

[0010] However, useful liquid chlorosilanes such as TCS and STC are also contained in the lower part of the distillation column to be disposed of about 95% by weight, and useful chlorosilanes are recovered from the disposed liquid. The development of an effective method was desired.

[0011] In order to solve the above problem, as one of the methods for concentrating chlorosilanes containing aluminum chloride to a higher concentration, there has been proposed an evaporator having a mechanism for evaporating and concentrating while scraping an evaporating surface with a scraper. .

[0012] However, even with this method, scaling cannot be completely prevented, and there is a problem in that the evaporation ability decreases with time due to scaling on the heating surface.

On the other hand, a sedimentation tank is provided below the reboiler of the distillation column, and a liquid having an aluminum chloride concentration of about 2% by weight or more due to evaporation of chlorosilanes is introduced into the sedimentation tank.
A method is shown in which the supersaturated aluminum chloride is precipitated and separated here by sedimentation to reduce scaling to the evaporator. Although this method has made some improvements in preventing scaling on the heat transfer surface, it has not been sufficiently solved.

[0014]

Accordingly, a method for recovering chlorosilanes from a chlorosilanes solution containing aluminum chloride by evaporation as described above,
It has been desired to develop a technology that almost completely eliminates scaling and blockage problems due to aluminum chloride on the heating surface and that can recover chlorosilanes with a high yield.

[0015]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, when chlorosilanes are evaporated and recovered from a chlorosilane solution containing aluminum chloride, the concentration of aluminum chloride in the concentrate is reduced. Exceeds 2% by weight of the conventionally known precipitation limit,
It was found that there was a state in which aluminum chloride hardly precipitated as a solid for minutes.

When a conventional distillation column is used, a concentrate having an aluminum chloride concentration of more than 2% by weight is retained as a bottom liquid, and almost all of the supersaturated portion of aluminum chloride is removed while circulating through a reboiler or the like. Seems to precipitate in the tower, causing problems such as blockage of the apparatus due to the scaling.

The present inventors have further studied based on the above findings. As a result, the chlorosilanes containing aluminum chloride can be reduced in residence time of the liquid to be treated, and using a thin film evaporator having good evaporation efficiency, by the thin film evaporation method, and under the condition that the concentrate is taken out in a liquid state. If chlorosilanes are recovered from the liquid by evaporation, the generation of scaling on the heating surface can be prevented extremely effectively, and stable recovery can be performed for a long period of time. It has been found that the recovery rate can be achieved, and the present invention has been completed.

That is, the present invention provides a method for recovering chlorosilanes by evaporating the chlorosilanes from a liquid containing aluminum chloride, wherein the chlorosilanes are evaporated by a thin film evaporation method, and the aluminum chloride concentrate is converted into a liquid. And recovering chlorosilanes.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a chlorosilane solution to be subjected to a thin film evaporation method is a condensate of chlorosilanes obtained by chlorination or hydrochlorination using metallurgical grade silicon as a raw material, and chlorosilanes from the condensate. , A liquid concentrate obtained by partially recovering by another distillation method.

The above-mentioned chlorosilanes liquid may contain all of the aluminum chloride contained in a dissolved state, or may be a state in which a part of the aluminum chloride is precipitated and contains a solid. A typical example of the chlorosilane liquid containing such a solid is a liquid concentrate obtained by partially recovering the above chlorosilanes by another distillation method. When the above concentrate is supplied as a chlorosilane liquid to the thin film evaporation method, after sufficiently precipitating aluminum chloride present in the liquid by supersaturation by distillation, the thin film evaporation method is carried out in a state containing the solid substance as the precipitate. It is preferred to apply.

The aluminum chloride content in the chlorosilanes solution obtained as a condensate in the chlorosilanes production process depends on the aluminum content in the metallurgical grade silicon used, the reaction conditions for the production of the chlorosilanes,
And the concentration in other distillation devices.

In the present invention, the concentration of aluminum chloride in the chlorosilanes solution used for the thin film evaporation method is desirably 80% by weight or less, which is a preferable upper limit of the concentrate described later. In consideration of the above, the upper limit is 50% by weight, preferably 30% by weight, more preferably 10% by weight, and most preferably 2% by weight.
% By weight. The lower limit of the aluminum chloride content is 0.01% by weight.

The method for producing a chlorosilane solution used in the present invention will be described more specifically as follows. For example, metallurgical grade silicon powder and chlorine-containing gas
A method of performing a chlorination reaction at 0 ° C. or higher, generally at 100 to 500 ° C., by mixing metallurgical grade silicon powder and a hydrogen chloride-containing gas
A method of performing a chlorination reaction at 50 ° C. or higher, generally 250 to 450 ° C., or a mixed gas of metallurgical grade silicon powder, STC and hydrogen at 400 ° C. or higher, generally 400 to 6 ° C.
A method of performing a hydrochlorination reaction at a temperature of 00 ° C. is generally known.

In these reactions, gases to be reacted with metallurgical grade silicon can be mixed and reacted with each other, or they can be mixed and reacted with an inert gas such as hydrogen or nitrogen. Is also possible.

The chlorosilanes solution obtained by condensing the chlorosilanes gas thus obtained is usually contained in a chlorosilanes solution of 0.1 g.
It contains from 01 to 2% by weight of aluminum chloride.

Of course, in the present invention, the chlorosilanes liquid may contain the other chlorides and silicon fine powder other than aluminum chloride.

In the present invention, in the thin film evaporation method, a known thin film evaporator capable of forming a thin film of a liquid to be treated on a heated surface and evaporating a liquid component can be used without any particular limitation.

Typical thin film evaporators include a stirring type thin film evaporator in which internal blades rotate to form a thin film with respect to a fixed heating surface (evaporation surface), and a centrifugal thin film type in which a heating surface rotates. An evaporator is mentioned.

The above-mentioned thin film evaporator has a vertical type and a horizontal type according to the rotation axis direction, a fixed blade type and a movable blade type according to the manner of mounting the blades on the rotation shaft, and further, the blades contact the evaporation surface. It is classified into a contact blade type and a non-contact blade type depending on whether it is performed or not. These methods can be used in an appropriate combination.

Among the more preferable types, a vertical contact movable blade type and a vertical non-contact blade type can be exemplified.
These thin film evaporators have a relatively excellent effect of suppressing scaling. In particular, the vertical contact movable blade type has the highest effect of suppressing scaling because the blade contacts the evaporation surface.

In the above-mentioned thin film evaporator, if the evaporating gas component is accompanied by droplets depending on the operating conditions, the removal rate of aluminum chloride may be reduced. In such a case, it is effective to install a droplet collector at the vapor outlet of the thin film evaporator as a means for preventing the entrainment of the droplet into the condenser. The droplet collector may be of any type as long as it can collect and remove droplets. For example, a baffle plate type and a centrifugal separation type are mentioned.

If the thin film evaporator has a movable blade in contact, the peripheral speed of the blade tip is preferably 0.1 m / s or more, preferably 0.5 m / s or more, and more preferably 1 m / s or more. is there. Further, the frequency of migration of the blade at one point on the evaporation surface is once or more per second, preferably once or more every 0.5 seconds, more preferably once or more every 0.3 seconds, This is preferable in that a sufficient scale suppressing effect is exhibited.

On the other hand, in the case of the vertical non-contact blade type, since the blade does not come into contact with the evaporating surface, it is necessary to rotate at a higher speed than the blade contact type, and the peripheral speed at the blade tip is 1 m / s or more. , Preferably 3 m / s or more, more preferably 5 m / s or more. Further, the frequency of migration of the blade at one point on the evaporation surface is at least once every 0.5 seconds, preferably at least once every 0.3 seconds, more preferably at least once every 0.1 seconds, Suitable conditions may be appropriately adopted according to the heat transfer area, the blade type, and the like.

The scaling prevention effect of aluminum chloride in the present invention is largely attributable to the reduction of the residence time in the apparatus by using a thin film evaporator.
At the same time, the effect of preventing the scaling by selecting the structure of the thin film evaporator or the operating conditions described above works synergistically, so that the scaling can be more effectively prevented.

In the present invention, when the chlorosilane liquid is supplied to the thin film evaporator, the liquid is heated while forming a liquid film on the evaporation surface, and the chlorosilanes evaporate, while concentration occurs on the liquid side.

In this way, the concentrate is taken out from the outlet of the evaporator, and the chlorosilanes recovered from the gas outlet are taken out in gaseous form.

In this case, the residence time of the liquid in the evaporator from the supply of the chlorosilane liquid to the removal of the concentrate is usually about 1 minute or less at most in a vertical thin film evaporator. Within minutes, even if the concentration of aluminum chloride in the concentrate exceeds the above-mentioned 2% by weight, precipitation of new aluminum chloride is almost prevented, and scaling to the evaporation surface can be effectively prevented.

In the case of the horizontal type, the stay time can be adjusted to some extent, but it is preferable to adjust the stay time within the above 10 minutes, preferably within 5 minutes.

The operating conditions for the above thin film evaporation include:
The heating medium temperature, the operating pressure, etc. may be mentioned, but these may be appropriately controlled according to the composition, supply amount, heat transfer area, concentration ratio, etc. of the chlorosilanes to be treated, as in the conventional evaporation operation. Conditions can be adopted.

At this time, the temperature of the aluminum chloride was about 180 ° C.
In order to effectively reduce the aluminum chloride content in the recovered chlorosilanes, the temperature of the concentrate at the outlet of the thin film evaporator is 180 ° C. or lower, preferably 1 ° C.
It is preferable to set the evaporation conditions so as to be 50 ° C. or lower.

In the present invention, by utilizing the above-mentioned special behavior of aluminum chloride with respect to the chlorosilanes solution, the concentrate obtained after the evaporation is allowed to contain aluminum chloride to a very high concentration, but the concentrate is dried. If it is hardened, there will be no function of washing out partially scaled or solid contents contained from the beginning, and the scale will be intense, and even if the scraping type thin film evaporator is used, continuous processing will be difficult. Become.

Therefore, in the present invention, it is necessary to carry out the thin-film evaporation under the condition that the obtained concentrate remains liquid. In particular, a suitable upper limit for the concentration of aluminum chloride in the concentrate is 80% by weight, preferably 50% by weight, more preferably 40% by weight.

The lower limit is set to 3% by weight, which is difficult to concentrate according to the prior art, and further to 10% by weight.
This is preferable because the effects of the present invention can be sufficiently exhibited.

The chlorosilanes recovered by the method of the present invention can be purified by a known distillation method or a known rectification method, if necessary, and used as a raw material for producing silicon.

As a device for carrying out the above distillation or distillation, a separate device may be provided, or if there is a facility for treating the same type of chlorosilanes in existing facilities, it may be used.

On the other hand, the concentrate may be treated by a known detoxification method, for example, neutralization with an alkali, hydrolysis with water, or the like.

Prior to the above treatment, the chlorosilanes may be recovered by separating the precipitated aluminum chloride by a known separation means such as filtration and centrifugation.

[0048]

As will be understood from the above description, according to the present invention, it is possible to recover chlorosilane by evaporation at a high recovery rate from a chlorosilane solution containing aluminum chloride.
It is possible to carry out the method without lowering the heat conductivity on the heating surface due to scaling and without blocking the device, which is an industrially extremely advantageous method.

[0049]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

The recovery rate and the aluminum chloride removal rate were determined as follows.

1. Recovery rate The supply amount of chlorosilanes and the recovered amount of evaporated components (kg /
H) was calculated from the following equation.

Recovery rate (%) = [recovered amount of evaporated component / supplied amount of chlorosilane liquid] × 100 Aluminum chloride removal rate The aluminum chloride concentration in the chlorosilanes supply liquid and the evaporating component recovery liquid was measured, and the amount of aluminum chloride in the chlorosilanes supply liquid and the amount of aluminum chloride (kg / H) in the evaporating component recovery liquid were determined. It was calculated by the following equation.

[0053]

(Equation 1)

3. Aluminum chloride concentration measurement Accurately weigh chlorosilanes to be measured in a container,
At 50 ° C. or lower, the chlorosilanes are sufficiently evaporated and removed while flowing the space above the chlorosilanes solution with a sufficiently dried inert gas. Dilute hydrochloric acid was added to the evaporation residue to dissolve the aluminum chloride, followed by filtration. The filtrate was quantified with an ICP (high frequency inductively coupled plasma) emission spectrophotometer or the like, and the amount was determined by dividing by the amount of the liquid before evaporation. Was.

Example 1 A heating medium jacket of a contact movable blade type vertical thin film evaporator having a heat transfer area of 0.15 m ² and an inner diameter of 0.15 m was previously heated to 102 ° C. by steam. Next, after setting the rotation speed so that the peripheral speed becomes 3 m / s, a chlorosilanes solution (TCS 19% by weight, ST
(77% by weight of C, 3% by weight of high-boiling silanes, 1% by weight of aluminum chloride) were supplied at 109 kg / H.

The weight of the recovered liquid in which the evaporated gas was liquefied by the condenser, the concentrated liquid discharged from the lower part of the thin film evaporator, and the aluminum chloride concentration were measured.

As a result, the amount of the evaporated component recovered liquid was 95 kg /
H, the amount of the concentrate was 14 kg / H, the concentration of aluminum chloride in the evaporating component recovery liquid was 0.06% by weight, the concentration of aluminum chloride in the concentrate was 7.4% by weight, the recovery rate was 87%, and the aluminum chloride removal rate was 95%. .

After 50 hours, there was no change in the recovery rate and the aluminum chloride removal rate. When the inside of the thin film evaporator was inspected, almost no scaling was observed.

COMPARATIVE EXAMPLE 1 The inner diameter was 1.2 m, the lower part was conical, and the heat transfer area was 3.5 m.
^2. An evaporator with a liquid holding volume of 0.8 m ³ was used. The heat transfer surface is scraped off with a scraper at a maximum peripheral speed of 3 m / s.
The evaporation surface jacket was heated with steam at 105 ° C. Chlorosilanes at a temperature of 55 ° C. (TCS 19% by weight, STC
(77% by weight, 3% by weight of high-boiling silanes, 1% by weight of aluminum chloride) were supplied so that the liquid holding amount was constant, and the contents were extracted from the lower part of the evaporator at a flow rate of 100 kg / H. The evaporated gas was liquefied by a condenser to obtain a recovered liquid.

As a result, the initial supply amount was about 1,300 k
g / H, but fell to about 800 kg / H after 50 hours. During this period, the average concentration of aluminum chloride in the recovered evaporating component solution was 0.04% by weight, the concentration of aluminum chloride in the concentrate was 10.1% by weight, the recovery rate was 90%, and the aluminum chloride removal rate was 96%.

After that, when the evaporator was inspected, a large amount of scaling occurred on the evaporating surface, and cleaning was required.

As described above, in the evaporator of the type in which the liquid stays for a long time, even if the evaporation surface is scraped off by a scraper, the prevention of scaling is not complete, and the processing capacity is temporally reduced by scaling the evaporation surface. You can see that it goes down.

Examples 2 to 6 Evaporation was carried out in the same manner as in Example 1 except that the supply amount of chlorosilanes and the jacket temperature were changed to the conditions shown in Table 1. The results obtained are shown in Table 1.

[0064]

[Table 1]

Examples 7 to 9 Evaporation was carried out in the same manner as in Example 1 except that the composition of the chlorosilanes was changed to the conditions shown in Table 2. Table 2 shows the obtained results.

[0066]

[Table 2]

Example 10 An evaporation operation was performed in the same manner as in Example 1 except that the evaporator was a non-contact movable blade type vertical thin film evaporator and the peripheral speed was changed to 10 m / s. .

As a result, 93 kg /
H, the amount of the concentrate was 16 kg / H, the concentration of aluminum chloride in the evaporating component recovery liquid was 0.06% by weight, the concentration of aluminum chloride in the concentrate was 6.4% by weight, the recovery rate was 85%, and the aluminum chloride removal rate was 94%. .

Further, there was no change in the recovery rate and the aluminum chloride removal rate after 50 hours had passed. When the inside of the thin film evaporator was inspected, no scaling was observed.

Claims (3)

[Claims] 1. A method for evaporating and recovering chlorosilanes from a chlorosilanes solution containing aluminum chloride, the method comprising evaporating the chlorosilanes by a thin film evaporation method and extracting a concentrate of aluminum chloride in a liquid state. Characteristic method for recovering chlorosilanes. 2. The recovery method according to claim 1, wherein the chlorosilanes contain aluminum chloride generated when a gas containing chlorine or hydrogen chloride or silicon tetrachloride and hydrogen is reacted with metallurgical grade silicon. 3. The method according to claim 1, wherein the content of aluminum chloride in the concentrate is adjusted to 3 to 80% by weight.